Method for carbon nanotube composite structure

ABSTRACT

A method for making a carbon nanotube composite structure is related. A substrate having a first surface is provided. A carbon nanotube structure including a plurality of carbon nanotubes is placed on the first surface, wherein the plurality of carbon nanotubes is in direct contact with the first surface. A monomer solution is coated to the carbon nanotube structure, wherein the monomer solution is formed by dispersing a monomer into an organic solvent. The monomer is polymerized, and then the substrate is removed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. § 119 from China Patent Application No. 201710365100.8, filed on May 22, 2017, in the China Intellectual Property Office, the disclosure of which is incorporated herein by reference.

FIELD

The present application relates to a method for making a carbon nanotube composite structure.

BACKGROUND

Carbon nanotubes are a novel carbonaceous material having extremely small size and extremely large specific surface area. Carbon nanotubes have interesting and potentially useful electrical and mechanical properties, and have been widely used in various fields such as emitters, gas storage and separation, chemical sensors, and high strength composites.

The composite of carbon nanotubes and polymer can be formed by two methods. One method includes dispersing the carbon nanotubes into an organic solvent to form a carbon nanotube dispersion, mixing the carbon nanotube dispersion and a monomer solution, and polymerizing the monomer. However, the carbon nanotubes have poor dispersion in the organic solvent, which affects the uniformity of the carbon nanotubes in the carbon nanotube composite structure. Another method includes completely melting the polymer, and mixing the melted polymer and the carbon nanotubes. However, the carbon nanotubes have poor dispersion in the melted polymer because the melted polymer has greater viscosity. Thus, the uniformity of the carbon nanotubes in the carbon nanotube composite structure is still poor.

What is needed, therefore, is to provide a method for making a carbon nanotube composite structure that can overcome the above-described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by way of example only, with reference to the attached figures, wherein:

FIG. 1 is a schematic process flow of one embodiment of a method for making a carbon nanotube composite structure.

FIG. 2 is a scanning electron microscope (SEM) image of a drawn carbon nanotube film.

FIG. 3 is an SEM image of a flocculated carbon nanotube film.

FIG. 4 is an SEM image of a pressed carbon nanotube film including a plurality of carbon nanotubes arranged along a same direction.

FIG. 5 is an SEM image of a pressed carbon nanotube film including a plurality of carbon nanotubes which is arranged along different directions.

FIG. 6 is an SEM image of a forth surface of a CNT/PI composite structure.

FIG. 7 is an SEM image of the forth surface of the CNT/PI composite structure coated with a gold film.

FIG. 8 is an atomic force microscope (AFM) image of the forth surface of the CNT/PI composite structure.

FIG. 9 is an AFM image of the forth surface of the CNT/PI composite structure coated with a gold film.

FIG. 10 is a schematic process flow of another embodiment of a method for making a carbon nanotube composite structure.

FIG. 11 is a schematic process flow of yet another embodiment of a method for making a carbon nanotube composite structure.

FIG. 12 is a schematic process flow of yet another embodiment of a method for making a carbon nanotube composite structure.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to illustrate details and features better. The description is not to be considered as limiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now be presented.

The term “substantially” is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. For example, substantially cylindrical means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like.

The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.

Referring to FIG. 1, a method for making a carbon nanotube composite structure 130 of one embodiment includes the following steps:

S1, placing a carbon nanotube structure 110 on a first surface 102 of a substrate 100, wherein the carbon nanotube structure 110 has a second surface 112 and a third surface 114 opposite to the second surface 112, and the third surface 114 is in direct contact with the first surface 102;

S2, coating a monomer solution 140 on the carbon nanotube structure 110, wherein the monomer solution 140 is formed by dispersing a certain amount of monomers into an organic solvent;

S3, polymerizing the monomer; and

S4, removing the substrate 100.

In the step S1, the carbon nanotube structure 110 includes a plurality of carbon nanotubes 118 uniformly distributed therein. A gap 116 is defined between adjacent carbon nanotubes 118. The plurality of carbon nanotubes 118 is parallel to the second surface 112 and the third surface 114. The plurality of carbon nanotubes 118 is parallel to the first surface 102. The plurality of carbon nanotubes 118 can be combined by van der Waals attractive force. The carbon nanotube structure 110 can be a substantially pure structure of the carbon nanotubes 118, with few impurities. The plurality of carbon nanotubes 118 may be single-walled, double-walled, multi-walled carbon nanotubes, or their combinations. The carbon nanotubes 118 which are single-walled have a diameter of about 0.5 nanometers (nm) to about 50 nm. The carbon nanotubes 118 which are double-walled have a diameter of about 1.0 nm to about 50 nm. The carbon nanotubes 118 which are multi-walled have a diameter of about 1.5 nm to about 50 nm.

The plurality of carbon nanotubes 118 in the carbon nanotube structure 110 can be orderly or disorderly arranged. The term ‘disordered carbon nanotube 118’ refers to the carbon nanotube structure 110 where the carbon nanotubes 118 are arranged along many different directions, and the aligning directions of the carbon nanotubes 118 are random. The number of the carbon nanotubes 118 arranged along each different direction can be almost the same (e.g. uniformly disordered). The carbon nanotubes 118 can be entangled with each other. The term ‘ordered carbon nanotube 118’ refers to the carbon nanotube structure 110 where the carbon nanotubes 118 are arranged in a consistently systematic manner, e.g., the carbon nanotubes 118 are arranged approximately along a same direction and/or have two or more sections within each of which the carbon nanotubes 118 are arranged approximately along a same direction (different sections can have different directions). The carbon nanotube structure 110 can be a carbon nanotube layer structure including a plurality of drawn carbon nanotube films, a plurality of flocculated carbon nanotube films, or a plurality of pressed carbon nanotube films.

Referring to FIG. 2, the drawn carbon nanotube film includes a plurality of successive and oriented carbon nanotubes 118 joined end-to-end by van der Waals attractive force therebetween. The carbon nanotubes 118 in the drawn carbon nanotube film extend along the same direction. The carbon nanotubes are parallel to a surface of the drawn carbon nanotube film. The drawn carbon nanotube film is a free-standing film. The drawn carbon nanotube film can bend to desired shapes without breaking. A film can be drawn from a carbon nanotube array to form the drawn carbon nanotube film.

If the carbon nanotube structure 110 includes at least two stacked drawn carbon nanotube films, adjacent drawn carbon nanotube films can be combined by only the van der Waals attractive force therebetween. Additionally, when the carbon nanotubes 118 in the drawn carbon nanotube film are aligned along one preferred orientation, an angle can exist between the orientations of carbon nanotubes 118 in adjacent drawn carbon nanotube films, whether stacked or adjacent. An angle between the aligned directions of the carbon nanotubes 118 in two adjacent drawn carbon nanotube films can be in a range from about 0 degree to about 90 degrees. Stacking the drawn carbon nanotube films will improve the mechanical strength of the carbon nanotube structure 110, further improving the mechanical strength of the carbon nanotube composite structure 130. In one embodiment, the carbon nanotube structure 110 includes two layers of the drawn carbon nanotube films, and the angle between the aligned directions of the carbon nanotubes 118 in two adjacent drawn carbon nanotube films is about 90 degrees.

Referring to FIG. 3, the flocculated carbon nanotube film includes a plurality of long, curved, disordered carbon nanotubes 118 entangled with each other. The flocculated carbon nanotube film can be isotropic. The carbon nanotubes 118 can be substantially uniformly dispersed in the flocculated carbon nanotube film. Adjacent carbon nanotubes 118 are acted upon by van der Waals attractive force to obtain an entangled structure. Due to the carbon nanotubes 118 in the flocculated carbon nanotube film being entangled with each other, the flocculated carbon nanotube film has excellent durability, and can be fashioned into desired shapes with a low risk to the integrity of the flocculated carbon nanotube film. Further, the flocculated carbon nanotube film is a free-standing film.

Referring to FIGS. 4 and 5, the pressed carbon nanotube film includes a plurality of carbon nanotubes 118. The carbon nanotubes 118 in the pressed carbon nanotube film can be arranged along a same direction, as shown in FIG. 4. The carbon nanotubes 118 in the pressed carbon nanotube film can be arranged along different directions, as shown in FIG. 5. The carbon nanotubes 118 in the pressed carbon nanotube film can rest upon each other. An angle between a primary alignment direction of the carbon nanotubes 118 and a surface of the pressed carbon nanotube film is about 0 degree to approximately 15 degrees. The greater the pressure applied, the smaller the angle obtained. If the carbon nanotubes 118 in the pressed carbon nanotube film are arranged along different directions, the pressed carbon nanotube film can have properties that are identical in all directions substantially parallel to the surface of the pressed carbon nanotube film. Adjacent carbon nanotubes 118 are attracted to each other and are joined by van der Waals attractive force. Therefore, the pressed carbon nanotube film is easy to bend to desired shapes without breaking. Further, the pressed carbon nanotube film is a free-standing film.

The term “free-standing” includes, but not limited to, the drawn carbon nanotube film, the flocculated carbon nanotube film, or the pressed carbon nanotube film that does not have to be supported by a substrate. For example, the free-standing the drawn carbon nanotube film, the flocculated carbon nanotube film, or the pressed carbon nanotube film can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. So, if the free-standing the drawn carbon nanotube film, the flocculated carbon nanotube film, or the pressed carbon nanotube film is placed between two separate supporters, a portion of the free-standing the drawn carbon nanotube film, the flocculated carbon nanotube film, or the pressed carbon nanotube film, not in contact with the two supporters, would be suspended between the two supporters and yet maintain film structural integrity.

The first surface 102 of the substrate 100 is very smooth. The height difference between the highest position of the first surface 102 and the lowest position of the first surface 102 is nanoscale. The height difference between the highest position of the substrate surface 102 and the lowest position of the substrate surface 102 can be defines as a smoothness of the substrate surface 102. The smoothness can also be greater than or equal to 0 nanometers and less than or equal to 30 nanometers. The smoothness can be greater than or equal to 0 nanometers and less than or equal to 20 nanometers. The smoothness can be greater than or equal to 0 nanometers and less than or equal to 10 nanometers. The material of the substrate 100 should be sapphire, monocrystalline quartz, gallium nitride, gallium arsenide, silicon, graphene, or polymer. The melting point of the substrate 100 needs to be greater than the temperature of polymerizing the monomer. The length, width, and thickness of the substrate 100 are not limited. In one embodiment, the substrate 100 is a silicon wafer.

Some organic solvent can be dripped on the second surface 112 of the carbon nanotube structure 110. When the organic solvent is volatilized, the air between the carbon nanotube structure 110 and the first surface 102 can be removed under the surface tension of the organic solvent. Thus, the carbon nanotube structure 110 can be tightly bonded to the first surface 102 of the substrate 100. The organic solvent can be ethanol, methanol, acetone, dichloroethane, or chloroform.

In the step S2, the monomer can be any monomer that can be polymerized to form a polymer 120. The polymer 120 includes a phenolic resin (PF), an epoxy resin (EP), a polyurethane (PU), a polystyrene (PS), a polymethylmethacrylate (PMMA), a polycarbonate (PC), polyethylene terephthalate (PET), phenylcyclobutene (BCB), polycycloolefin or polyimide (PI), polyvinylidene fluoride (PVDF), and the like. In one embodiment, the monomer is an imide, and the polymer 120 is a polyimide. The organic solvent includes ethanol, methanol, acetone, dichloroethane or chloroform.

The monomer solution 140 has a small viscosity and good fluidity. When the monomer solution 140 is coated on the second surface 112 of the substrate 100, the monomer solution 140 can pass through the gaps 116 and contact with a part of the first surface 102. The first part of the substrate 102 is in direct contact with and coated by the monomer solution 140, the second part of the substrate surface 102 is in direct contact with the carbon nanotubes 118. The method for coating the monomer solution 140 is not limited and can be spin coating, injection coating, or the like. In one embodiment, the monomer solution 140 is coated on the carbon nanotube structure 110 by spin coating.

In the step S3, the method for polymerizing the monomer is not limited, such as high temperature treatment. In one embodiment, the substrate 100 and the carbon nanotube structure 110 coated with the monomer solution 140 are placed in a reaction furnace. The reaction furnace is heated to the temperature of polymerizing the monomer, and the monomer is polymerized to form the polymer 120. The part surface of the carbon nanotube 118, that is directly contacted with the first surface 102 of the substrate 100, is defined as a contact surface 117. Because the carbon nanotubes 118 are tubular, the third surface 114 of the carbon nanotube structure 110 is in fact a ups and downs surface. The contact surface 117 is parts of the third surface 114. Except for the contact surface 117, the rest of third surface 114 is in direct contact with the monomer solution 140. The gaps 116 are filled with the monomer solution 140. When the monomer is polymerized to form the solid polymer 120, the polymer 120 is combined with the carbon nanotube structure 110 to form the carbon nanotube composite structure 130.

In the step S4, the method for removing the carbon nanotube composite structure 130 from the first surface 102 of the substrate 100 is not limited. The carbon nanotube composite structure 130 can be peeled off from the first surface 102 of the substrate 100 by water immersion, blade, tape, or other tools.

The smoothness of the substrate surface 102 is nanoscale, thus the contact surface 117 can be in direct contact with the substrate surface 102 during coating the monomer solution 140 and polymerizing the monomer. Thus, there is no monomer solution 140 between the contact surface 117 and the first surface 102 during coating the monomer solution 140 and polymerizing the monomer. Thus, when the carbon nanotube composite structure 130 is peeled from the first surface 102, the contact surface 117 is exposed and is not coated by the polymer 120. A part of outer wall of the carbon nanotube 118 directly contacting with the first surface 102 is exposed and is not covered by the polymer 120. Except for the contact surface 117, the rest of the outer walls of carbon nanotubes 118 are coated by and in direct contact with the polymer 120.

The carbon nanotube composite structure 130 includes the plurality of carbon nanotubes 118 and the polymer 120. The plurality of carbon nanotubes 118 are uniformly dispersed in the polymer 120. The plurality of carbon nanotubes 118 can be joined end-to-end and extend along the same direction. The plurality of carbon nanotubes 118 can also extend along different directions, or entangled with each other to form a network-like structure. The carbon nanotube composite structure 130 has a forth surface 132. The forth surface 132 is in direct contact with the first surface 102 before peeling the carbon nanotube composite structure 130 off from the substrate 100. The length direction of the plurality of carbon nanotubes 118 is parallel to the forth surface 132. The surface of the polymer 120 near the substrate 100 is defined as a lower surface 122. The contact surface 117 and the lower surface 122 together form the forth surface 132. Thus, the contact surface 117 is a part of the forth surface 132 and exposed from the polymer 120. The contact surface 117 is an exposed surface and can protrude out of the lower surface 122 of the polymer 120. The height difference between the exposed surface and the lower surface 122 of the polymer 120 is nanoscale. Since the smoothness of the first surface 102 is at nanoscale level, the forth surface 132 is also smooth at nanoscale level. The height difference between the contact surface 117 and the lower surface 122 can be greater than or equal to 0 nanometers and less than or equal to 30 nanometers. The height difference between the contact surface 117 and the lower surface 122 can be greater than or equal to 0 nanometers and less than or equal to 20 nanometers. The height difference between the contact surface 117 and the lower surface 122 can also be greater than or equal to 0 nanometers and less than or equal to 10 nanometers.

In one embodiment, the polymer 120 is polyimide, the carbon nanotube structure 110 is two stacked drawn carbon nanotube films, and the angle between the aligned directions of the carbon nanotubes 118 in two adjacent drawn carbon nanotube films is about 90 degrees.

In one embodiment, to synthesize poly(amic acid) (PAA) solution, 2.0024 g of ODA (10 mmol) was placed in a three-neck flask containing 30.68 mL of anhydrous DMAc under nitrogen purge at room temperature. After ODA is completed dissolved in DMAc, 2.1812 g of PMDA (10 mmol) is added in one portion. Thus, the solid content of the solution is about 12%. The mixture is stirred at room temperature under nitrogen purge for 12 h to produce a PAA solution. The two stacked drawn carbon nanotube films are located on a silicon wafer, wherein the angle between the aligned directions of the carbon nanotubes 118 in two adjacent drawn carbon nanotube films is about 90 degrees. Then the PAA solution is coated on the two stacked drawn carbon nanotube films, and the PAA solution will gradually penetrate into the two stacked drawn carbon nanotube films to form a preform. The preform is thermal imidized in muffle furnace at 80° C., 120° C., 180° C., 300° C., and 350° C. for 1 h respectively to form a CNT/PI composite structure. Finally, the CNT/PI composite structure is peeled off from the silicon wafer.

FIG. 6 is an SEM image of the first composite structure surface of a CNT/PI composite structure. As shown in FIG. 6, the carbon nanotubes 118 are uniformly dispersed in the CNT/PI composite structure.

FIG. 7 is an SEM image of the first composite structure surface of the CNT/PI composite structure coated with a gold film, and the thickness of the gold film is about 1 nm. As shown in FIG. 7, the forth surface 132 is a smooth surface with no ups and downs from the naked eye. The height difference between the highest position of the forth surface 132 and the lowest position of the forth surface 132 is nanoscale. FIG. 8 is an atomic force microscope (AFM) image of the first composite structure surface of the CNT/PI composite structure. FIG. 9 is an AFM image of the first composite structure surface of the CNT/PI composite structure coated with a gold film, and the thickness of the gold film is about 3 nm. As shown in FIG. 8 and FIG. 9, it is also find that the forth surface 132 is a smooth surface.

Referring to FIG. 10, a method for making a carbon nanotube composite structure 160 of another embodiment includes the following steps:

S21, placing the carbon nanotube structure 110 on the first surface 102 of the substrate 100, wherein the carbon nanotube structure 110 has the second surface 112 and the third surface 114 opposite to the second surface 112, and the third surface 114 is in direct contact with the first surface 102;

S22, locating a graphene layer 150 on the second surface 112;

S23, coating a monomer solution 140 on the graphene layer 150 and the carbon nanotube structure 110, wherein the monomer solution 140 is formed by dispersing the monomer into the organic solvent;

S24, polymerizing the monomer; and

S25, removing the substrate 100.

In this embodiment, the method for making the carbon nanotube composite structure 160 is similar to the method for making the carbon nanotube composite structure 130 above except that the graphene layer 150 is located on the second surface 112 before coating the monomer solution 140.

The graphene layer 150 is a two dimensional film structure. If the graphene layer 150 includes a plurality of graphene films, the plurality of graphene films can overlap each other to form a large area. The graphene film is a one-atom thick planar sheet composed of a plurality of sp²-bonded carbon atoms. The graphene layer 150 can be a free-standing structure. The term “free-standing structure” means that the graphene layer 150 can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. So, if the graphene layer 150 is placed between two separate supports, a portion of the graphene layer 150 not in contact with the two supports, would be suspended between the two supports and yet maintain structural integrity. When the plurality of graphene films overlap each other, a gap is formed between adjacent two graphene films. During coating the monomer solution 140, the monomer solution 140 can pass through the graphene layer 150 and the carbon nanotube structure 110 to arrive at the first surface 102, because both the graphene layer 150 and the carbon nanotube structure 110 have gaps 106.

Referring to FIG. 11, a method for making a carbon nanotube composite structure 170 of yet another embodiment includes the following steps:

S31, placing the carbon nanotube structure 110 on the first surface 102 of the substrate 100 to form a preform structure 172, wherein the carbon nanotube structure 110 has the second surface 112 and the third surface 114 opposite to the second surface 112, and the third surface 114 is in direct contact with the first surface 102;

S32, locating two preform structures 172 on a base 174, wherein the two preform structures 172 are spaced from each other, the substrates 100 of the two preform structures 172 and the base 174 form a mold 176 having an opening, and the carbon nanotube structures 110 of the two preform structures 172 are opposite to each other and inside of the mold 176;

S33, injecting the monomer solution 140 into the inside of the mold 176 from the opening of the mold 176, wherein the monomer solution 140 is formed by dispersing the monomer into the organic solvent;

S34, polymerizing the monomer; and

S35, removing the substrates 100 and the base 174.

In this embodiment, the method for making the carbon nanotube composite structure 170 is similar to the method for making the carbon nanotube composite structure 130 above except the steps S32 and S33.

In the step S32, the method for making the mold 176 is not limited. For example, the two preforms structures 172 and the base 174 are fixed together by sticking or mechanically fastening to form the mold 176. In one embodiment, the two preforms structures 172 and the base 174 are fixed by a sealant, and the sealant is 706B vulcanized silicon rubber. The opening is on the top of the mold 176. The carbon nanotube structure 110 of each of the two preforms structures 172 is located inside of the mold 176. The substrate 100 of each of the two preforms structures 172 forms the sidewall of the mold 176. The material of the base 174 is not limited, such as glass, silica, metal or metal oxide. In one embodiment, the material of the substrate 174 is glass. The carbon nanotube structure 110 in the mold 176 would not fall off from the substrate 100 because the carbon nanotube structure 110 itself has viscosity. The organic solvent can be dripped so that the carbon nanotube structure 110 is firmly adhered to the substrate 100.

Furthermore, the length or width of the carbon nanotube structure 110 can be greater than the length or width of the first surface 102. When the carbon nanotube structure 110 is disposed on the first surface 102, the excess carbon nanotube structure 110 can be folded into the back surface of the substrate 100, and an adhesive can be applied to the back surface of the substrate 100. Thus, the carbon nanotube structure 110 in the mold 176 is firmly adhered to the substrate 100 and would not fall off from the substrate 100. The back surface is opposite to the first surface 102, and the first surface 102 can be considered the front surface. The melting point of the adhesive needs to be greater than the temperature of polymerizing the monomer.

In the step S33, the monomer solution 140 is slowly injected into the inside of the mold 176 along the inner wall of the mold 176. The monomer solution 140 completely submerges the carbon nanotube structure 110. The monomer solution 140 would not break the integrity of the carbon nanotube structure 110 during injecting the monomer solution 140 because the carbon nanotube structure 110 is supported by the substrate 100.

Referring to FIG. 12, a method for making a carbon nanotube composite structure 180 of yet another embodiment includes the following steps:

S41, placing the carbon nanotube structure 110 on the first surface 102 of the substrate 100, wherein the carbon nanotube structure 110 has the second surface 112 and the third surface 114 opposite to the second surface 112, and the third surface 114 is in direct contact with the first surface 102;

S42, placing the carbon nanotube structure 110 and the substrate 100 into a container 182, wherein the container 182 has an opening;

S43, injecting the monomer solution 140 into the container 182 from the opening of the container 182, wherein the monomer solution 140 is formed by dispersing the monomer into the organic solvent;

S44, polymerizing the monomer; and

S45, removing the substrates 100 and the container 182.

In this embodiment, the method for making the carbon nanotube composite structure 180 is similar to the method for making the carbon nanotube composite structure 130 above except the steps S42 and S43.

In the step S42, the container 182 has a bottom. When the carbon nanotube structure 110 and the substrate 100 are located in the container 182, the substrate 100 is located on and in direct contact with the bottom of the container 182. The carbon nanotube structure 110 is spaced from the bottom by the substrate 100. The material of the container 182 is not limited, such as silica, metal, glass, or metal oxide. In one embodiment, the material of the container 182 is glass.

In the step S43, the monomer solution 140 does not break the integrity of the carbon nanotube structure 110 during injecting the monomer solution 140 because the carbon nanotube structure 110 is supported by the substrate 100. The amount of the monomer solution 140 can be adjusted so that the monomer solution 140 submerges the entire carbon nanotube structure 110, or submerges only a part of the carbon nanotube structure 110. When the monomer solution 140 submerges only a part of the carbon nanotube structure 110, the thickness of the polymer 120 is less than the thickness of the carbon nanotube structure 110. Thus, in the carbon nanotube composite structure 180, some carbon nanotubes 118 are located in and completely coated by the polymer 120, and some carbon nanotubes 118 are exposed from and extend out of the polymer 120. In one embodiment, the carbon nanotube structure 110 includes three stacked drawn carbon nanotube films, and the monomer solution 140 submerges only a part of the carbon nanotube structure 110. In the carbon nanotube composite structure 180, the first drawn carbon nanotube film, the second drawn carbon nanotube film and the third drawn carbon nanotube film are stacked. The second drawn carbon nanotube film is between the first drawn carbon nanotube film and the third drawn carbon nanotube film. The entire outer walls of the carbon nanotubes 118 in the second drawn carbon nanotube film are coated by the polymer 120. Partial outer wall of the carbon nanotubes 118 in the first drawn carbon nanotube film are exposed. The contact surfaces 117 of the carbon nanotubes 118 in the third drawn carbon nanotube film are exposed.

The monomer solution 140 has a smaller viscosity than the molten polymer, thus after coating the monomer solution 140 and polymerizing the monomer, the carbon nanotubes 118 can uniformly dispersed in the polymer 120. In above methods, the substrate 100 has a nanoscale smooth first surface 102, thus some carbon nanotubes of the carbon nanotube composites 130, 160, 170, and 180 are exposed from the polymer 120, improving the conductivity of the carbon nanotube composites 130, 160, 170, and 180.

The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in matters of shape, size and arrangement of the parts within the principles of the present disclosure up to, and including, the full extent established by the broad general meaning of the terms used in the claims.

Additionally, it is also to be understood that the above description and the claims drawn to a method may comprise some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps. 

What is claimed is:
 1. A method for making a carbon nanotube composite structure, the method comprising: providing a substrate having a first surface, wherein the first surface is a nanoscale smooth surface; placing a carbon nanotube structure comprising a plurality of carbon nanotubes on the first surface, wherein the plurality of carbon nanotubes is in direct contact with the first surface; disposing a monomer solution on the carbon nanotube structure, wherein the monomer solution is formed by dispersing monomers into an organic solvent; polymerizing the monomer, wherein the plurality of carbon nanotubes is in direct contact with the first surface during disposing the monomer solution and polymerizing the monomer; and removing the substrate.
 2. The method of claim 1, wherein a height difference between a highest position of the first surface and a lowest position of the first surface is greater than or equal to 0 nanometers and less than or equal to 30 nanometers.
 3. The method of claim 1, wherein a material of the substrate is sapphire, monocrystalline quartz, gallium nitride, gallium arsenide, silicon, graphene, or polymer.
 4. The method of claim 1, wherein the plurality of carbon nanotubes is joined end-to-end by van der Waals attractive force and extends substantially along the same direction.
 5. The method of claim 4, wherein the carbon nanotube structure comprises at least two carbon nanotube films, and an angle between the plurality of carbon nanotubes in the at least two carbon nanotube films is range from about 0 degree to about 90 degrees.
 6. The method of claim 1, wherein the plurality of carbon nanotubes is substantially parallel to the first surface.
 7. The method of claim 1, wherein a plurality of gaps is defined by the plurality of carbon nanotubes, and the monomer solution passes through the plurality of gaps and arrive at the first surface during disposing the monomer solution.
 8. The method of claim 1, wherein the substrate is a silicon wafer, the monomer is poly(amic acid), and the polymer is polyimide.
 9. The method of claim 1, further comprising locating a graphene layer on the carbon nanotube structure before disposing the monomer solution.
 10. The method of claim 1, wherein the monomer is polymerized to form a polymer, and some of the plurality of carbon nanotubes are exposed from the polymer after removing the substrate.
 11. The method of claim 1, wherein the disposing the monomer solution comprises placing the carbon nanotube structure and the substrate in a container and injecting the monomer solution in the container.
 12. A method for making a carbon nanotube composite structure, the method comprising: providing a substrate having a first surface, wherein the first surface is a nanoscale smooth surface; placing a carbon nanotube structure comprising a plurality of carbon nanotubes on the first surface to form a preform structure, wherein the plurality of carbon nanotubes is in direct contact with the first surface; locating two preform structures on a base, wherein the two preform structures are spaced from each other, the substrates of the two preform structures and the base form a mold having an opening, and the carbon nanotube structures of the two preform structures are opposite to each other and inside of the mold; injecting a monomer solution into the mold from the opening, wherein the monomer solution is formed by dispersing monomers into an organic solvent; polymerizing the monomer; and removing the substrates of the two preform structures and the base.
 13. The method of claim 12, wherein a height difference between a highest position of the first surface and a lowest position of the first surface is greater than or equal to 0 nanometers and less than or equal to 30 nanometers.
 14. The method of claim 12, wherein a material of the substrate is sapphire, monocrystalline quartz, gallium nitride, gallium arsenide, silicon, graphene, or polymer.
 15. The method of claim 12, wherein the plurality of carbon nanotubes is joined end-to-end by van der Waals attractive force and substantially extends along the same direction.
 16. The method of claim 15, wherein the carbon nanotube structure comprises two carbon nanotube films, and an angle between the plurality of carbon nanotubes in the two carbon nanotube films is range from about 0 degree to about 90 degrees.
 17. The method of claim 12, wherein the plurality of carbon nanotubes is substantially parallel to the first surface.
 18. The method of claim 12, wherein a plurality of gaps is defined by the plurality of carbon nanotubes, and the monomer solution passes through the plurality of gaps and arrive at the first surface during injecting the monomer solution.
 19. The method of claim 12, wherein the substrate is a silicon wafer, the monomer is poly(amic acid), and the polymer is polyimide. 